The present invention relates to a soft resin composition for injection molding and uses thereof. More particularly, the invention relates to a soft resin composition for injection molding, which is a polyolefin composition containing an ethylene/xcex1-olefin copolymer, and is capable of producing, with good productivity, an injection-molded product being excellent in flexibility, transparency and texture and being suitably used as soft toys and articles for daily use, etc., an injection-molded product thereof, and a coated product of such a product.
Polyolefins, such as relatively soft ethylene/xcex1-olefin copolymers having a Shore A hardness of 40 to 95, especially those having a Shore A hardness of 40 to 70, are of low crystallinity or amorphous to cause the following problems related to molding when they are injection-molded as being such a copolymer.
The problems related to molding are, specifically, that a molten resin filled in a desired mold through injection requires a long time to reach a hardened state sufficient to be released from the mold (such a time is referred to as xe2x80x9ccooling timexe2x80x9d hereinafter), and molded products have molding defects such as sinkmarks and flash. The time-consuming cooling time prolongs a molding cycle, resulting in a lowered productivity of injection-molded products. The occurrence of molding defects, such as sinkmarks and flash, increases an inferior injection-molded product rate. Molded products should avoid the occurrence of these defects. A soft ethylene/xcex1-olefin copolymer of lower crystallinity has a slower hardening rate and therefore tends to cause the above problems related to molding.
For the only purpose of increasing the hardening rate, a low crystalline or amorphous ethylene/xcex1-olefin copolymer can be blended with a filler such as an inorganic filler and a resin having a relatively high hardening rate such as high crystalline polypropylene and polyethylene. The above method, however, has a drawback in that the flexibility and the translucency inherent in the ethylene/xcex1-olefin copolymer are deteriorated, although the hardening rate of the ethylene/xcex1-olefin copolymer is increased.
There is no coatings or primers exhibiting good adhesion to the ethylene/xcex1-olefin copolymer, and therefore a molded product comprising the ethylene/xcex1-olefin copolymer is not suitable for uses that necessarily require coating.
Accordingly, there is desired a soft resin composition for injection molding, which is capable of producing, with good productivity, an injection-molded product excellent in translucency and appearance without substantially decreasing the transparency while maintaining flexibility inherent in the low crystalline or amorphous ethylene/xcex1-olefin copolymer, and an injection-molded product thereof and especially an injection molded product excellent in adhesion to coating.
The present invention has been made in order to solve the above problems related to the prior art, and an object of the present invention is to provide a soft resin composition for injection molding which is capable of producing, with good productivity, a translucent injection-molded product excellent in appearance without causing a substantial decrease of transparency while maintaining flexibility inherent in the low crystalline or amorphous ethylene/xcex1-olefin copolymer, and an injection-molded product thereof usable as soft toys and articles for daily use.
Another object of the invention is to provide an injection-molded product of the above properties, which have been subjected to color-finishing with a coating and is excellent in adhesion of coating.
The soft resin composition for injection molding of the present invention comprises:
(A) 94 to 99 parts by weight of an ethylene/xcex1-olefin copolymer comprising ethylene and an xcex1-olefin of 3 to 10 carbon atoms and having
(i) a Shore A hardness (JIS K 6253) of 40 to 95,
(ii) a melt flow rate (MFR2.16), as measured at 190xc2x0 C. under 2.16 kg load in accordance with ASTM D 1238, of 1.0 to 20 g/10 min, and
(iii) a density (ASTM D 1505) of 855 to 900 kg/m3; and
(B) 1 to 6 parts by weight of a polyethylene having
(i) a melt flow rate (MFP2.16), as measured at 190xc2x0 C. under 2.16 kg load in accordance with ASTM D 1238, of 0.1 to 100 g/10 min,
(ii) a density (ASTM D 1505) of 910 to 925 kg/m3, and
(iii) a melt tension measured at 190xc2x0 C. and the MFR2.16 satisfying the following relation:
melt tension greater than 2.2xc3x97(MFR2.16)xe2x88x920.84, 
wherein the sum of the component (A) and the component (B) is 100 parts by weight.
The soft resin composition for injection molding comprising the components (A) and (B) preferably has a Shore A hardness of 90 or less.
The soft resin composition for injection molding of the invention preferably has a ratio (HAB/HA) of the Shore A hardness (JIS K 6253) of the soft resin composition for injection molding (HAB) to the Shore A hardness (JIS K 6253) of the ethylene/xcex1-olefin copolymer (A) (HA) of 1.00 to 1.05.
The ethylene/xcex1-olefin copolymer (A) preferably has:
(iv) a molecular weight distribution (Mw/Mn), as determined by a gel permeation chromatography (GPC), of 1 to 3, and
(v) a ratio (MFR10/MFR2.16) of a melt flow rate (MFR10: g/10 min) as measured at 190xc2x0 C. under 10 kg load in accordance with ASTM D 1238 to the MFR2.16 (g/10 min) of 5 to 20.
The ethylene/xcex1-olefin copolymer (A) may be a mixture of at least two ethylene/xcex1-olefin copolymers (A).
The injection-molded product of the invention comprises the soft resin composition for injection molding described above.
The injection-molded product of the invention may have been subjected to coating on the surface.
The coated product is preferably an injection-molded product having been subjected to color-finishing with a coating material, the color-finishing being made by coating the surface of the above-mentioned injection-molded product with a primer comprising a styrene elastomer resin graft-polymerized with a monomer having an xcex1,xcex2-monoethylenically unsaturated group, and then conducting the coating.
Highly preferably, the coated product of the invention is an injection-molded product having been subjected to color-finishing with a coating material, the color-fishing being made by coating the surface of the above-mentioned injection-molded product with a mixture of the primer and a photopolymerization initiator, subjecting the coated surface to UV-ray treatment, and then conducting the coating.
The toys and the articles for daily use of the present invention comprise the above-mentioned injection-molded product.